Add missing Javadoc.
diff --git a/src/main/java/org/apache/commons/lang3/stream/Streams.java b/src/main/java/org/apache/commons/lang3/stream/Streams.java
index ef6612d..d9d6a2a 100644
--- a/src/main/java/org/apache/commons/lang3/stream/Streams.java
+++ b/src/main/java/org/apache/commons/lang3/stream/Streams.java
@@ -172,6 +172,11 @@
             return stream().anyMatch(Failable.asPredicate(predicate));
         }
 
+        /**
+         * Throws IllegalStateException if this stream is already terminated.
+         *
+         * @throws IllegalStateException if this stream is already terminated.
+         */
         protected void assertNotTerminated() {
             if (terminated) {
                 throw new IllegalStateException("This stream is already terminated.");
@@ -332,6 +337,11 @@
             stream().forEach(Failable.asConsumer(action));
         }
 
+        /**
+         * Marks this stream as terminated.
+         *
+         * @throws IllegalStateException if this stream is already terminated.
+         */
         protected void makeTerminated() {
             assertNotTerminated();
             terminated = true;